1. Field of the Invention
The present invention relates to a grinding machine for drill bits which are used as cutting tools and more particularly to a grinding machine for grinding the tip of a twisted drill bit.
2. Prior Art
In a twisted drill bit which has two spiral grooves on the shank, the intersecting portion formed by the grooves and the surface of the tip of the drill bit which is substantially cone shaped forms a cutting edge, and a work piece is cut by this cutting edge. In this type of drill bit, the cutting edge tends to break when used for a long period of time, and thus cutting performance also tends to decrease.
Accordingly, the tip of the drill bit must be ground after a certain period of use in order to maintain preferable cutting performance. When the drill bit is ground, it is necessary to grind the surface of the tip of the drill bit so that it can be formed into a predetermined shape. (Throughout the specification, the surface of the tip of the drill bit is called a rake angle surface, and the angle between this surface and an axial center of the drill bit is called the rake angle).
However, it is not easy to grind the tip end surface of the drill bit into the predetermined shape. Grinding is usually done by a drill bit grinding machine which is designed solely for grinding drill bits. However, this machine is relatively large and complex in structure. Grinding can also be accomplished by a skilled expert manually grinding the tip of the drill bit. There are no other reliable ways to grind the drill bit except the above-described two ways.
The problem with the drill bit grinding machine is that the machine is relatively expensive. On the other hand, when the drill bit is ground manually, the problem is that only a skilled expert can grind the tip of the drill bit into a predetermined shape.